This invention relates generally to a system of charging rechargeable batteries and more particularly to a battery charging system for a lithium electrode rechargeable battery which may be incompatible with earlier battery chargers.
Battery chargers usually contain all the circuitry needed to charge a battery except for sensing devices such as thermistors. Batteries typically contain no electrical circuitry except for sensing devices such as thermistors or type determining circuitry such as that described in U.S. patent application Ser. No. 341,778, "Method and Apparatus for Determining Battery Type", filed on behalf of Johnson et al. on 04/21/89. However, it has been noted that some designers have placed some active circuitry within the battery housing primarily to protect the electrochemical cells from damage due to accidental short circuits during transport or use.
Rechargeable batteries employing a lithium electrode generally provide a greater energy storage capacity per unit volume than other commercially available batteries used in portable products. A lithium battery is a desirable addition to such a portable product. Lithium batteries, however, have charging characteristics which are different than other types of rechargeable batteries.
When a new battery type becomes available, full compatibility between currently available battery chargers and the new battery type is usually not present; the new battery type connot be optimally charged by the chargers optimized for previously existing battery types.
Other charging systems exist using batteries which contain additional circuitry within the battery housing to accomplish temperature sensing of the electrochemical cells, which is coupled to the charger circuitry for modification of the charger performance. Any additional current drain placed on the battery by this circuitry causes reduced storage life for the battery. In order to reduce this additional current drain, expensive low power circuit elements have been used.